Strain relief for electrical connectors



March 26, 1940; L; L, L D'D- 2,195,113

STRAIN RELIEF FOR ELECTRICAL CONNECT-0R5 Filed April 10, 1937 Pawnee Mar. 26, 19 6 tannin STRAIN nnmnr l ggn E EU RIOALCON;

TORS

"Lester Liliadd, Lo'ckport,-Ill., assignortoflemzge "D. Lad'd, Imckp'ort, :Ill;

Application April 10, 1927, 'Serial'Nd. rssjr'ss My invention relates to electrical terminals and particularly to plug connectorssuch as are used for connecting conductor cords to electrical outlets and to electrical appliances.

Devices of this type usually comprise a body portion of insulating material having mounted therein or thereon a plurality of socket or pin type contacts. ','Ihe conductors or the electrical cord with which the connector is used are connected to the contacts by suitable screwsorthe like.

'During the use of appliance cords and similar devices, it is common practice to effect'the disconnection of the cord from the associated out- "let'o'r appliance by a pulling or jerking "action and, to assure reasonably satisfactory operation of the cord and connectorovera substantial period of time, "it is necessary to provide some means, in the nature of a-strain relief, for-preventing the stresses induced-bysuch pulling "or jerking from being transmitted to-the connection between the coi'd'conductors and' the connector contacts. In, fact, this matter is of such a serious nature,--both from the viewpoint of assuring "satisfactory long operative life of the connector and a minimization of firehazard, that the insurance underwriters have required thatan approved connector of the "above described type mustbe capable of sustaining a weight of twenty :poundsapplied across the contacts thereof and the associated cordxfor a periodof five minutes without causing'separation ofthe cord and the contacts, when the screws for fastening the cord conductors to the contacts havebeen backed off one'-half turn. j

' The main objects .of thepresentinvention are to provide an improved strain reliefof simple construction for mechanically interconnecting the cordiproper with the body :portion of the connectorso :as to prevent the stresses induced .duringuse of the *connectorfrom being transmitted to the electrical connection between the cord conductors andthe connector contacts; -to

provide an improved strain relief which may be.

embodied into existing connector plug structures without any modification thereof to provide an improved strain relief which may 'be applied =la-terally to the cord with which it is used; "and to provide an improved strain relief of the subl'ject' type which-shall utilize -a minimum'of parts and whichshall be inexpensive to manufacture and to install. a

An illustrative embodiment ofthe invention is shown inthe accompanying drawing, wherein-'- Figure "1 a side elevation ,parrtially broken means.

away of an appliance type connector plug utilizing a strain relief'inzaccordance with the-present invention;

Figure 2 is asectional view, partially in elevation, taken on the general line 2-"2 of Fig- ,5

ure 1;

FigureB isan enlargedplan view of the strain relief of the present invention as applied tothe conductor cord with whichiit is used;

Figure 4 is .a view similar Ilto v"Figure 3, but ,10 showing an intermediateipositionin the apply- :ing of the strain relief to the cord with which it is used;

Figure 5 is a sectional view onlthe general line 5--5 OfFigureB; 2115 Figure 6 is -a side elevationo-f 'thestrain relief applied to the .'conductor cord with whichlitlis used;

Figure '7 isa perspective view of the strain retlie f .in theassembledposition with its cord grip- :20 ping disks, open;

Figure-Bis'a perspective view of the two disks of the strain relief when disassembled.

"Figure 9 is a perspective view of a locking springwhichpreferably .fforms a part of Ithe strain relief; and r iEigure .1 10 is ..a side elevation, .partially.in section of a connector .cap, such asis commonly utilized at the outlet len'd' o-f an appliance cord, embodying a strain relief 'in accordance with the V ,present invention.

Referring'to the drawing, the appliance type .connector therein illustrated includes a suitable body or grip portion comprising vtwo complementary members l-which may be of .moldedinlsulating material and which are releasab-ly secured together, as by a bolt 2 orother suitable Suitable recesses} are'formed in the inner 'faces of. the'body forming members Iffor receiving a pair of socket type contacts 4 which,

are adapted to. releasablyengage the contact pins forming a part of-the appliance withwliich the connector is used. The conductors? of thecorfd '6 are connected toitheupper ends of these contact elements] by suitablescrews "l or similar 5 means;

To minimize'beriding andkinking of thecord adjacent the connector, the connector includes an axially flexible protector spring 8, thelower coilsf'S of which occupy an annular recess'lllisu "formed in the cooperating members I making up the body portion of thelconnector. Iffdesired,

the upper end of the lprotectorspring'ltl maybe provided withia ferrule H or insulating material encircling the cord proper.

position.

In the preferred embodiment of the invention shown, the strain relief comprises a pair of cord grips taking the form of apair of disks l2 and I3, with centrally located slots 14- and i5, respectively, in order that the disks may be appliedlaterally to the cord conductor with which the strain relief is used. The members [2 and i3 are preferably punched from sheet insulating material such as hard fiber. The slots i4 and 15 are of somewhat less Width than the normal diameter of the conductor cord, in order that the strain relief shall at least slightly compress and very tightly grip the conductor cord when in position thereon,- as is illustrated in Figure 5, and are formed with flaring openends to facilitate the entrance of the cord and with concave inner ends which hug opposite sides of the cord when the disks are fully closed on the cord as shown in Fig. 3.

The disks I2--l3 are hinged together by means, of a spring wire it which is bent to the form shown in Figures 3, 4, 5, 6, 7 and 9. The spring includes a hinge pin section ll which passes through apertures 53, is in the disks i2, i3, respectively, laterally opposite the slots. The extremity 2d of the spring, adjacent the hinge pin section, is bent against the disk l2 so as to secure the disks against accidental disengagement. The intermediate portion of the spring forms a clip 25 which is looped around a portion of the disk I? and extends into peripheral recesses 22, 23 formed in the disk 52 so as to lock the spring in proper position.

The end of the spring which is seated in the recess 23 forms a latch Zdwhich is adapted to enter a peripheral recess 25 in the disk l3 for locking the two disks in the assembled position shown in Figures 3, 5 and. 6. Adjacent the recess' 25, the periphery of the disk I3 is formed to provide a cam 25 which is adapted to engage the latch 24, as shown in Fig. 4, as the disks are pressed edgewise toward each other for urging thelatch outwardly so as to permit it to snap into the recess 25 when the recesses 23 and 25 are brought into alinement, as shown in Fig. 3.

With this improved construction," each of the washers or disks serves as a gate for closing the open end of the slot of the other disk.

The manner of attachingthe strain relief is illustrated particularly in Figures 3 and l. Either of the two disks l2 and i3 is applied laterally to the conductor cord at the desired location thereon and the other disk is then swung on its hinge into engagement with the cord.

.As the two disks approach the operative position, the cam 2G rides on the latch 2 so as to urge the latch outwardly until it snaps into the recess 25 for locking the parts in operative The proportions of the slots l4 and E5 in the two disks are, as mentioned previously, such that when those members are in the assembled position they very tightly grip the conductor cord with which the strain relief is used and, by virtue of the fact that the stresses induced in the spring is which'serve to latch the two disks together are of a shearing nature, there is no tendency'for the various elements of the strain relief to become disengaged during use thereof. If the strain relief is used in conjunction with an appliance type connector, such as that illustrated in the drawing, thej'outer dimensions of the strain relief arepreferably so proportioned that the strain relief may be fitted within the lowermost coils-9 of the protective spring 8 which prevents excessive bending of the conductor cord 6. When in that position the strain, relief will abuttingly engage the adjacent upper coils of that spring and will mechanically connect the conductor cord 3 to the body portion of the connector plug with a resilient connection. Thus, none "of the stresses which may be induced inthe cord 6 during use of the connector will be transmitted to the electrical connection between the cord conductors 5 and the socket terminals 4 of the connector.

When the strain relief is used in conjunction with other types of connectors, such as plug caps and the like, the proportions of the two disks maybe conveniently correlated with the dimensions of such other connectors to accomplish the desired mechanical interconnection of the cord and the connector. A particularly suitable arrangement is illustrated in Figure 10. The strain relief in this device abuttingly engages a suitable annular recess 27 formed in the body portion 23 of aplug cap 29.

From the foregoing, it'will be seen that I have be. applied laterally to the cord at any desired point, either before or after the cord conductors have been connected to the terminals with which they are used. The ability of being laterally applicable to the cord is of the greatest importance in minimizing assembling costs, and in making possible many of the most desirable features of the invention.

Although but one specific embodiment of the invention has been herein shown and described, it will be understood that details of the construction shown may be altered without departing from the spirit of my invention as defined by the following claims.

I claim: p

1. The combination with a compressible conductor cord, of a strain relief for application to said cord comprising a disk having an openended slot to permit said disk to be applied edge-- Wise to the cord,said slot being of less width than the diameter of said cord whereby. said disk-is adapted to pinch the cord, a gate for closing the open end of said slot 'to'secure said disk against removal from the cord, and a wire for locking said gate in closed position;- said wire having a portion embracing a portion of said disk, a portion formingaihinge pin for connecting said gate to said disk, and a portionseparably engaged with said gate to lock the latter in closed position.

2. The combination witha compressible conductor cord, of a strain relief for application to said cord comprising a disk having an open-ended slot to permit said disk to-be applied e'dgewise to the cord, said slot being of less width than the diameter of said cord whereby said disk is adapted to pinch the cord, a gate for closing the open end of said slot to secure said disk with a peripheral notch, and a spring wire for,

locking said gate in closed position, said wire having aninterr nediate' portion embracing a por tion of said disk one end portion forming a hinge pin'jor connecting said gate to said disk, and its other end portion serving as a latch cooperating with said notch for automatically looking said gate in closed position. I

3. A strain relief for application to a cord comprising a pair of overlapping fiat cord grips having opposed-open-ended slots for receiving the cord, each of said grips servingas a gate for closing the open end of the opposedslot, and a p ing wire embracing a portion or one of said ips, said spring wire having a portion serving as a hinge pin for hingedly'conn'eoting said grips 15 together and having another portion serving as a resilient latch for locking said ,gripsin operative position. h p I 4. The combination with a-compressible con- "ductor cord, of a strain relief for application to as to permit its disk to pinch the cord, each of said disks servingas a gate for closing the open end of the'opposedslot, and a spring wire embracinga portion of one of said disks, said wire having a portion serving as a hinge pin for pivotally connecting said disks to each other.

. l LESTER. L. LADD. 

